2. Global drainage direction map


The 30’ global drainage direction map DDM30





Former versions



The global drainage direction map DDM30 is a raster map which describes the drainage directions of surface water with a spatial resolution of 30’ longitude by 30’ latitude. 66896 individual grid cells, covering the entire land surface of the globe (without Antarctica), are connected to each other by their respective drainage direction and are thus organized into drainage basins. Each cell can drain only into one of the eight neighboring cells. DDM30 is based on 1) the digital drainage direction map with a resolution of 5’ of Graham et al. (1999) for South America, Australia, Asia and Greenland, and 2) the HYDRO1k digital drainage direction map (as flow accumulation map) with a resolution of 1 km (USGS, 1999) for North America, Europe, Africa and Oceania (without Australia). Both given base maps were upscaled to a resolution of 30’. The resulting drainage direction map was manually corrected using the vectorized river data sets of ESRI (1992) and ESRI (1993), various atlases and the location and drainage basin sizes of 935 river discharge gauging stations from the GRDC (1999). In the course of the manual corrections, the drainage directions of 35% of the grid cells were changed.


The map is generated with a cellsize of 30 arc minutes and is distributed as a zipped ASCII-grid that can be easily imported in most GIS-software that support rasters or grids. The direction of outflow from cell is according to the ArcInfo/ArcView convention as follows: "0" is assigned to internal sinks and to cells draining into the ocean while "1", "2", "4", "8", "16", "32", "64" and "128" standing for the outflow directions E, SE, S, SW, W, NW, N or NE.


Routing of water in global hydrological models at a resolution of 30 arc minutes.

Data download


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drainage, global map, drainage direction, hydrology, global modelling, water, river flow

Please cite as

"Döll, P., Lehner, B. (2002): Validation of a new global 30-minute drainage direction map. Journal of Hydrology, 258(1-4), 214-231."